#!/usr/bin/perl 
# reverse.pl
use strict;
use warnings;

my %hash = ('Key1' => 'Value1', 'Key2' => 'Value2');
print "$hash{Key1}\n";   # print 'Value1'
foreach (keys %hash) {
   # invert key-value pair
   $hash{$hash{$_}} = $_;

   # remove original key
   delete $hash{$_};
}
print "$hash{Value1}\n";   # print 'Key1'